In general, color filters used in solid state camera devices, liquid crystal display devices and the like are based on a transparent substrate, with color elements arranged thereon, for example, in mozaic structures, stripes, or triangles.
Currently these color filters are mainly produced using a dyeing technique.
In the dyeing technique, a dyeable water-soluble polymer such as gelatin, fish glue, casein, or polyacrylamide is mixed with a bichromate salt or a water-soluble azide to make it photosensitive, which is then irradiated through a photomask and developed with water to obtain a relief pattern. The relief pattern is dyed to form a colored image. This process is repeated three times to form red, green, and blue filters. Between the individual processes, the filter is, for example, resist treated with tannic acid, or provided with an intermediate layer of urethane resin or acrylic resin to prevent color mixing.
However, such a prior art dyeing method has problems in that (1) the process is complicated, (2) it is difficult to control the dyeing bath, (3) the dyed medium (water-soluble polymer) is inferior in heat resistance, and (4) the dye is inferior in heat resistance and weather resistance.
To overcome such disadvantages, recent development of color filter is being actively conducted using such techniques as a printing method or a pigment dispersion method.
The printing method uses an ink comprising a pigment dispersed in an organic vehicle, which is printed onto a transparent substrate to form a colored image. This method allows film formation and patterning to be simultaneously carried out, is simple in process, and is superior in durability. However, this method involves new problems such as (1) fringing, (2) poor dimensional accuracy, and (3) poor surface smoothness.
The pigment dispersion method has improved the above problems. In this method, a pigment is dispersed in a photosensitive resin, which is coated onto a transparent substrate, exposed, and developed to form a colored image. This method can produce a color filter by a simple process compared to the dyeing method. As photosensitive resins used in the pigment dispersion method, there have been proposed various types of resins such as stilbazolium group-pendant polyvinylalcohol disclosed in Japanese Patent Publication Laid-open 60-124738/1985, photosensitive polyimide and polyamide disclosed in Japanese Patent Publication Laid-open 60-237403/1985 and Japanese Patent Publication Laid-open 62-212603/1987, a photosensitive resin comprising an acrylic polymer and bis-diazide compound disclosed in Japanese Patent Publication Laid-open 1-200353/1989, and a radical polymerization type photosensitive resin comprising a multifunctional acrylate monomer, an organic polymer binder, and a photopolymerization initiator disclosed in Japanese Patent Publication Laid-open 1-152449/1989.
However, of these photosensitive resins used in the pigment dispersion method, the stilbazolium group-pendant polyvinylalcohol is inferior in heat resistance. To improve this problem, Japanese Patent Publication Laid-open 2-160807/1990 proposes stilbazolium group-pendant polyvinylalcohol having a betaine structure, however, this substance is still insufficient in heat resistance.
Furthermore, a photosensitive resin using a photosensitive polyimide or polyamide has a high heat resistance, however, involves problems such as: (1) the resin is colored, (2) the resin is low in sensitivity, and (3) it must be developed with an organic solvent. A system using bis-azide compounds as a photosensitive agent (1) is low in sensitivity, and (2) tends to be affected by oxygen during exposure. A system using radical polymerization is high in sensitivity but tends to be affected by oxygen during exposure. To prevent this, the resin must be exposed in an inert gas atmosphere or an oxygen barrier film must be provided, which requires use of an expensive device or a complex process.
With a view to eliminate such prior art problems, it is a primary object of the present invention to provide a photosensitive colored resin composition which (1) is high in sensitivity, (2) is not affected by oxygen, (3) is superior in heat resistance, and (4) can be developed with an aqueous developer. Another object of the present invention is to provide a colored image formation method for a color filter by using the inventive photosensitive colored resin composition to form successive patterns of the color filter.
The color filter normally has B (blue), R (red), and G (green) picture elements arranged on a transparent substrate. To obtain an image of good contrast, it is necessary to form a black matrix which is a light blocking between the picture elements. In an active type display device using a switching device, in particular, this light blocking film can remove unnecessary light, thereby reducing misoperation due to light from the switching device.
Prior art formation methods of the black matrix include (1) patterning a dyeable synthetic resin and dyeing with a black dye, (2) formation by printing, and (3) deposition of a metal such as chromium.
However, the prior art formation methods of black matrix have the following problems:
The dyeing method of (1) is difficult to obtain a sufficient density and complex in process.
The printing method of (2) is simple with reduced process steps, butt is low in precision of fine lines and positioning and difficult to obtain a sufficient density.
The deposition method of (3) is very costly.
Therefore, in order to maintain the lightness of the entire image and obtain a high-precision image and the black matrix formation, a formation method is in demand which can provide a sufficient density to block light and enables high-precision fine lines at a low cost.
With a view to eliminate the above prior art problems, it is another object of the present invention to provide a formation method of a low-cost black matrix which has a sufficient light blocking ability, is high in precision, and involves reduced process steps.